1. Field of the Invention
The present invention relates to a device for continuous unbalanced mass adjustment in steerable vibration plates, the device having an actuating element that is formed as a piston of a hydraulic cylinder and that stands in a working connection with the associated unbalance mass, a storage unit for hydraulic fluid, and a pressure source that comprises a delivery pump for the hydraulic fluid.
2. Description of the Related Art
Vibration plates that are suitable for use as soil compacting devices are set into vibration by rotating unbalanced masses. Through rotation of the unbalanced masses relative to one another, it is known to modify the resulting forces that occur and their direction of action, and in this way to influence the travel speed of the vibration plate and its direction of motion. Up to now, the adjustment of the two unbalanced masses has taken place using a respective single-acting hydraulic cylinder to which there is allocated a return spring in order to produce the restoring force. In this way, in theory the manipulated variable allocated to each hydraulic cylinder can be set arbitrarily by increasing the pressure in each of the two cylinders until the spring has undergone a defined shortening, in accordance with its spring characteristic, and, in this position on the piston that can be moved in the cylinder, creates an equilibrium between hydraulic force and spring force.
However, in practical operation, this equilibrium of forces is disturbed, and restoring moments are superposed on it that are neither constant nor linear and thus cannot be compensated. Causes of this can be for example restoring moments of the drive motor and/or reaction forces of the soil; an oscillation of the spring can occur, or effects of the inertia of the piston can become effective if the machine is exposed to extreme impacts.
From EP-A-0 070 345, an unbalance vibrator is known that has an adjustable flyweight. The unbalance vibrator has two unbalance shafts that can rotate in directions counter to one another, of which one has a fixedly attached flyweight and the other has a cylinder oriented transversely to the unbalance shaft. In the cylinder, a piston that acts as a flyweight is housed. Optionally, a pressure medium can be provided to the one side or the other side of the piston, and the piston can thereby be pressed into an end position. When pressure impinges on the piston from both sides, the piston can be hydraulically locked in its middle position. The unbalance vibrator can be used in a vibration plate for modifying the direction of travel in the forward and backward direction.